Started by Bryce, 15:34, 08 June 12
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Quote from: Bryce on 11:16, 14 June 12Correct (MacDeath) the sound output (Pin 6) on the cassette player isn't connected. But the Op-Amp for this also isn't present. I could easily add this, but I suspect you (MrLou) will opt not to want this, because the intended use is mainly for music and you have already mentioned your dis-like of the humming on the sound output of the 464. This is probably why Amstrad chose to remove it. Having a non shielded wire routed from the tape deck on the right all the way over to the AY on the left is probably a major source of humming on the output. And do you really need to hear the tape loading? Is it worth having a humming in the speaker? I could connect it to its own speaker, not connected to the normal sound output at all? That would avoid the humming, but I will need to find a space in the CPC.
Quote from: Bryce on 13:53, 14 June 12The Classic 464 actually uses a very indirect way of making those sounds. The Tapedeck isn't actually connected directly to the speaker anywhere. The data leaving the tape PCB is already in a digital form and is passed through the AY and back to the speaker as far as I know. So the Firmware / CPU must play some part in linking the two.Bryce.
Quote from: Bryce on 16:42, 14 June 12Ah... So on a 6128 with external tape player you hear the sounds too? That would prove that it's not leakage and IS being produced by the AY. The wire from the tape socket of the 6128 goes directly to B7 of the PIO and definitely isn't connected to anything else.Bryce.
Quote from: Bryce on 16:23, 14 June 12Due to the lack of physical connection, I assume that the CPU is reading B7 and writing whatever is required to the AY. Do you have a dis-assembled version of the loading sequence we could look at?Bryce.
;; sample edge and check for escapecpu is in a tight loop sampling the input.BTW:If you have a tape player connected *WITHOUT* motor control, and you turn up the volume, and you don't start the loading process. You can STILL hear it through the speaker.It is also true if you just do this from basic:out &f600,&10So, leave it on Ready prompt, turn it up and listen... So now, where is the sound comming from???
Quote from: Bryce on 11:18, 15 June 12I wasn't suggesting that the analogue signal is magically getting sent to a non-existant analogue input on the AY. I was suggesting that the CPU (which is reading the 0s and1s at B7 of the 8255) is running a small routine to tell the AY to play note X when a 0 is read and play note Y when a 1 is read. The reason for this conclusion is the schematics, which as you can see below (this time the 6128), the wire from the tape port goes directly to the 8255 input B7. It's not (according to the schematics) connected to anything else and has no direct route to the speaker.The "noise gate" you describe is the part I called Op-Amp B in the diagram above. If I get time at the weekend, I'll open up a 464 and a 6128 and check if there are any connections there, that are not on the schematics. Last night while doing some more of the 464+ mod (the original theme of this thread ) I found several errors in the schematics and the BOM.Bryce.
Quote from: arnoldemu on 11:38, 15 June 12@Bryce: The CPU doesn't do what you suggest.There is nothing in the loading/saving which does this.What I would like to know on a cpc is the SOUND on the expansion, does it have tape noise or not?It is possible it doesn't, and that only the speaker has the extra connection.As for the errors in the schematics it would be great, when you have time to correct them.
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